The invention relates to assembly of small electromechanical packages. More particularly, it relates to the precision alignment of optical structures to optical fibers or alignment features within optoelectronic or semiconductor packages.
Micro-electromechanical systems (hereinafter xe2x80x9cMEMSxe2x80x9d) integrate micro-mechanical structures with micro-electronic circuits to produce an integrated device. Because of their small size, MEMS have many useful applications. For example, MEMS have been implemented as mirrors within optical devices to redirect light beams, as accelerometers used to deploy air bags in automobiles, as well as for micro-machined gyroscopes, motors, and pumps.
One of the biggest challenges in optical MEMS packaging is high precision alignment. Typically, MEMS devices require that a micro-mechanical die have a highly precise position with respect to various associated input and output elements. xe2x80x9cHighly precise positionxe2x80x9d as the term is used herein, refers a position accurate to within less than one micron. For example, alignment of MEMS elements to optical fibers or light beams from other sources is required to be typically accurate within a fraction of one micron. There are various techniques to actively align optical fibers in use in the industry and described in academic literature.
Related to MEMS devices are optoelectronic packages, which contain one or more passive and/or active optical elements in a structure produced using techniques similar to conventional semiconductor fabrication processes. The term xe2x80x9cmicrostructurexe2x80x9d is used herein to generically refer to MEMS and/or optoelectronic devices.
A microstructure device can be attached in a package or holder using various techniques including conventional silicon die attachment processes. Typical semiconductor packaging tolerances for die attachment are on the order of tens of microns, with some technologies capable of approximately 5 microns. Achieving sub-micron positional accuracies is non-trivial.
Current approaches perform a passive positional alignment of the microstructure device during the die attachment process. Subsequently, the optical fiber or light source is actively aligned to the microstructure element. Such approaches are typically very slow and relatively expensive.
A microstructure package and a method of assembling such a package are described. A package base provides an outer body of the package and has an internal cavity. A device die is located within the cavity, mounted to a flexible die attach paddle, and the flexible die attach paddle connects the base and the die. The paddle is then immovably fixed to hold the die in a highly precise position relative to the base.
An adhesive material may be used to immovably fix the paddle, which may be made, for example, of a Kovar-type metal alloy, copper, copper alloy, Alloy 42, Invar, stainless steel, or nickel alloy. The adhesive material may include, without limitation, solder, glass, or epoxy. The die may be further wirebonded to the base to provide electrical connection. In various specific embodiments, the die may be either an active or passive optical device.
The package may further include a package cover having an optical window, wherein the paddle is immovably fixed such that the die has a highly precise position relative to the optical window or to some other relative reference position. If the package has one or more optical fibers attached, then the paddle is immovably fixed such that the die has a highly precise position relative to the fiber or fibers.
In specific embodiments, the die may be a two- or three-dimensional MEMS array. A two dimensional array refers to an out of plane MEMS structure where the MEMS mirrors have two states (binary) either in the plane of the die surface or out of the die surface plane. There can be 1xc3x971 to Nxc3x97N mirrors in this structure. A three dimensional array refers to an in-plane MEMS structure that can be moved to different positions by rotation in the plane of the die surface. The package may be a conventional semiconductor package, a butterfly-type package, some other standard or variant of an optical or optoelectronic package, or a custom package.